Biamperometric detection

The Karl Fischer procedure has now been simplified and the accuracy improved by modification to a coulometric method (Chapter 14). In this procedure the sample under test is added to a pyridine-methanol solution containing sulphur dioxide and a soluble iodide. Upon electrolysis, iodine is liberated at the anode and reactions (a) and (b) then follow the end point is detected by a pair of electrodes which function as a biamperometric detection system and indicate the presence of free iodine. Since one mole of iodine reacts with one mole of water it follows that 1 mg of water is equivalent to 10.71 coulombs. 

Danet, A. F, David, V., and David, I. Acetaminophen determination by flow injection analysis with biamperometric detection, Rei. Roum. Chim. 43(9) 811-816, 1998. 

E.V. Aquino, J.J.R. Roohwedder, C. Pasquini, A new approach to flow-batch titration. A monosegmented flow titrator with coulometric reagent generation and potentio-metric or biamperometric detection, Anal. Bioanal. Chem. 386 (2006) 1921. 

Nitrite Nitrite is an important indicator of fecal pollution in natural waters as well as a potential precursor of carcinogenic species. A rush of flow and sequential injection spectrophotometric method based on Griess-type reactions has been proposed, also coupled to online sorbent enrichment schemes. The catalytic effect of nitrite on the oxidation of various organic species constitutes the basis of fairly sensitive spectrophotometric methods. Fluorometric methods based on the formation of aromatic azoic acid salts, quenching of Rhodamine 6G fluorescence, and direct reaction with substituted tetramine or naphthalene species have been also reported. Indirect CL methods usually involve conversion into nitric oxide and gas-phase detection as mentioned in the foregoing section. The redox reaction between nitrite and iodide in acidic media is the fundamental of a plethora of flow injection methodologies with spectrophotometric, CL, or biamperometric detection. New electrochemical sensors with chemically modified carbon paste electrodes containing ruthenium sites, or platinum electrodes with cellulose or naphthalene films, have recently attracted special attention for amperometric detection. 

Hulanicki, A., W. Matuszewski, and M. Trojanowicz. 1987. Flow injection determination of nitrite and nitrate with biamperometric detection at two platinum wire electrodes. Anal. Chim. Acta 194 119-127. 

Cheregi, M. and A. F. Danet. 1997. Flow injection determination of L-ascorbic acid in natural juice with biamperometric detection. Anal. Lett. 30 2625-2640. 

A biamperometric method for the direct determination of pyrogallol compounds was based on the electrocatalytic oxidation of pyrogallol compounds at one pretreated platinum electrode and the reduction of platinum oxide at the other pretreated platinum electrode to form a biamperometric detection system with an applied potential difference of 10 mV. Three important compounds detected by the method were pyrogallol, gallic acid, and tannic acid. The linear relationships between currents and the concentrations of pyrogallol, gallic acid, and tannic acid were determined over the ranges 1.0 x 10 -1.0 X 10, 1.0 X 10 -1.0 X 10 and 1.0 x 10 -2.0 x 10 mol with detection limits... 

If it is desired to use the biamperometric method for detecting the end point, then the calomel electrode and also the silver rod (if used) must be removed and replaced by two platinum plates 1.25 cm x 1.25 cm. The potentiometer (or pH meter) used to measure the e.m.f. must also be removed, and one of the indicator electrodes is then joined to a sensitive galvanometer fitted with a variable shunt. The indicator circuit is completed through a potential divider... 

Verhoef and co-workers suggested omitting the foul smelling pyridine completely and proposed a modified reagent, consisting of a methanolic solution of sulphur dioxide (0.5 M) and sodium acetate (1M) as the solvent for the analyte, and a solution of iodine (0.1 M) in methanol as the titrant the titration proceeds much faster and the end-point can be detected preferably bipoten-tiometrically (constant current of 2 pA), but also biamperometrically (AE about 100 mV) and even visually as only a little of the yellow sulphur dioxide-iodide complex S02r is formed (for the coulometric method see Section 3.5). 

In this automatic system, the authors preferably used coulometric generation of titrant (cf., microcoulometric determination of deviations in the above end-point titration ), e.g., H, OH, Ag, Hg2+, Br2,12, Fe(CN) (cf., Table 1 in ref. 63). The detection method may be potentiometric (logarithmic signal), amperometric (linear signal), biamperometric, conductometric, oscillometric, etc. Moreover, the authors evaluated triangle programmed titration curves by... 

Silver sulfadiazine is dissolved in dilute hydrochloric acid and determined by titration with sodium nitrite solution (assay of the primary aromatic amine function). The endpoint detection is commonly biamperometric (27). 

Modern coulometric titrators commonly use electrochemical detection, either potentiometric or biamperometric. These are readily implemented with electronic circuitry that is compatible with the devices used to produce the controlled current. Biamperometry was first applied to end-point detection by Swift and co-workers (30), potentiometry by Epstein et al. (14), both in 1947. 

The constant-current generation of bromine is carried out in a medium of dichloroacetic acid, hexafluoroisopropanol, water, potassium bromide and mercury(II)chloride. To this medium an amount of the polymer, previously dissolved in hexafluoroisopropanol and diluted with anhydrous dichloroacetic acid, is added and bromine generated. The end of the reaction is detected biamperometrically. The suitability of this method was tested against methyl vinyl terephthalate. 

Note BA biamperometric titration CE-CCD capillary electrophoresis with contactless conductivity detection CL chemiluminescence EB electrochemical biosensor FAAS flame atomic absorption spectrometry FIA flow injection analysis HPLC-UV high-performance liquid chromatography with UV detection MC multicommutation P potentiometry SIA sequential injection analysis SP spectrophotometry TB turbidimetry. 

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